The present invention relates to a printer, such as an inkjet printer, having an improved recording medium feeding mechanism.
An inkjet printer records images on a recording medium sheet, that is fed along a sheet feeding path, with a print head which moves across the sheet in a direction perpendicular to the sheet feeding path.
An inkjet printer usually includes a feed roller and a discharge roller for feeding the sheet along the sheet feeding path, and the print head is located between the two rollers. A platen is opposingly arranged below the print head at a distance from the print head appropriate for inkjet printing. A plurality of pinch rollers are opposingly arranged above the discharge roller to guide the sheet therebetween.
In such an inkjet printer, when the leading end of the sheet is fed beyond the discharge roller, it tends to rotate along the circumferential periphery of the discharge roller. As a result, the trailing end of the sheet tends to float on the platen which causes deterioration of printing quality.
The rotation of the discharge roller is usually adjusted such that the peripheral velocity thereof becomes slightly higher than that of the feed roller. The difference in the peripheral velocities of the two rollers applies tension to the sheet therebetween and keeps the sheet from slacking and/or floating on the platen. The feeding velocity of the sheet, however, changes when the trailing end of the sheet has passed the feed roller and the sheet becomes to be fed only by the discharge roller. Such change of feeding velocity is not desirable since this also causes deterioration of the printing quality.
Usually, the feed roller and the discharge roller are held by supporting members located beside the sheet feeding path, and are rotatably driven by a single driving mechanism that is mounted to one of the supporting members. The supporting member supporting the driving mechanism is located apart from the space, within which the print head moves during printing, in order to avoid interference between the driving mechanism and the print head. Accordingly, the distance between the supporting members, and therefore the length of the discharge roller held by the supporting members, are relatively long.
Since longer rollers generally require higher strength against bending and twisting, the shaft of the long discharge roller is made of metal to obtain the required strength. However, the use of a metal shaft is one of the causes that make cost reduction of the printer difficult.